#

#  Copyright (c) 1995-2001, Raphael Manfredi

#  Copyright (c) 2002-2014 by the Perl 5 Porters

#  Copyright (c) 2015-2016 cPanel Inc

#  Copyright (c) 2017 Reini Urban

#

#  You may redistribute only under the same terms as Perl 5, as specified

#  in the README file that comes with the distribution.

#

require XSLoader;

require Exporter;

package Storable;

our @ISA = qw(Exporter);

our @EXPORT = qw(store retrieve);

our @EXPORT_OK = qw(

	nstore store_fd nstore_fd fd_retrieve

	freeze nfreeze thaw

	dclone

	retrieve_fd

	lock_store lock_nstore lock_retrieve

        file_magic read_magic

	BLESS_OK TIE_OK FLAGS_COMPAT

        stack_depth stack_depth_hash

);

our ($canonical, $forgive_me);

our $VERSION = '3.11';

our $recursion_limit;

our $recursion_limit_hash;

do "Storable/Limit.pm";

$recursion_limit = 512

  unless defined $recursion_limit;

$recursion_limit_hash = 256

  unless defined $recursion_limit_hash;

BEGIN {

    if (eval {

        local $SIG{__DIE__};

        local @INC = @INC;

        pop @INC if $INC[-1] eq '.';

        require Log::Agent;

        1;

    }) {

        Log::Agent->import;

    }

    #

    # Use of Log::Agent is optional. If it hasn't imported these subs then

    # provide a fallback implementation.

    #

    unless ($Storable::{logcroak} && *{$Storable::{logcroak}}{CODE}) {

        require Carp;

        *logcroak = sub {

            Carp::croak(@_);

        };

    }

    unless ($Storable::{logcarp} && *{$Storable::{logcarp}}{CODE}) {

	require Carp;

        *logcarp = sub {

          Carp::carp(@_);

        };

    }

}

#

# They might miss :flock in Fcntl

#

BEGIN {

    if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) {

        Fcntl->import(':flock');

    } else {

        eval q{

	          sub LOCK_SH () { 1 }

		  sub LOCK_EX () { 2 }

	      };

    }

}

sub CLONE {

    # clone context under threads

    Storable::init_perinterp();

}

sub BLESS_OK     () { 2 }

sub TIE_OK       () { 4 }

sub FLAGS_COMPAT () { BLESS_OK | TIE_OK }

# By default restricted hashes are downgraded on earlier perls.

$Storable::flags = FLAGS_COMPAT;

$Storable::downgrade_restricted = 1;

$Storable::accept_future_minor = 1;

XSLoader::load('Storable');

#

# Determine whether locking is possible, but only when needed.

#

sub CAN_FLOCK; # TEMPLATE - replaced by Storable.pm.PL

sub show_file_magic {

    print <

#

# To recognize the data files of the Perl module Storable,

# the following lines need to be added to the local magic(5) file,

# usually either /usr/share/misc/magic or /etc/magic.

#

0	string	perl-store	perl Storable(v0.6) data

>4	byte	>0	(net-order %d)

>>4	byte	&01	(network-ordered)

>>4	byte	=3	(major 1)

>>4	byte	=2	(major 1)

0	string	pst0	perl Storable(v0.7) data

>4	byte	>0

>>4	byte	&01	(network-ordered)

>>4	byte	=5	(major 2)

>>4	byte	=4	(major 2)

>>5	byte	>0	(minor %d)

EOM

}

sub file_magic {

    require IO::File;

    my $file = shift;

    my $fh = IO::File->new;

    open($fh, "<", $file) || die "Can't open '$file': $!";

    binmode($fh);

    defined(sysread($fh, my $buf, 32)) || die "Can't read from '$file': $!";

    close($fh);

    $file = "./$file" unless $file;  # ensure TRUE value

    return read_magic($buf, $file);

}

sub read_magic {

    my($buf, $file) = @_;

    my %info;

    my $buflen = length($buf);

    my $magic;

    if ($buf =~ s/^(pst0|perl-store)//) {

	$magic = $1;

	$info{file} = $file || 1;

    }

    else {

	return undef if $file;

	$magic = "";

    }

    return undef unless length($buf);

    my $net_order;

    if ($magic eq "perl-store" && ord(substr($buf, 0, 1)) > 1) {

	$info{version} = -1;

	$net_order = 0;

    }

    else {

	$buf =~ s/(.)//s;

	my $major = (ord $1) >> 1;

	return undef if $major > 4; # sanity (assuming we never go that high)

	$info{major} = $major;

	$net_order = (ord $1) & 0x01;

	if ($major > 1) {

	    return undef unless $buf =~ s/(.)//s;

	    my $minor = ord $1;

	    $info{minor} = $minor;

	    $info{version} = "$major.$minor";

	    $info{version_nv} = sprintf "%d.%03d", $major, $minor;

	}

	else {

	    $info{version} = $major;

	}

    }

    $info{version_nv} ||= $info{version};

    $info{netorder} = $net_order;

    unless ($net_order) {

	return undef unless $buf =~ s/(.)//s;

	my $len = ord $1;

	return undef unless length($buf) >= $len;

	return undef unless $len == 4 || $len == 8;  # sanity

	@info{qw(byteorder intsize longsize ptrsize)}

	    = unpack "a${len}CCC", $buf;

	(substr $buf, 0, $len + 3) = '';

	if ($info{version_nv} >= 2.002) {

	    return undef unless $buf =~ s/(.)//s;

	    $info{nvsize} = ord $1;

	}

    }

    $info{hdrsize} = $buflen - length($buf);

    return \%info;

}

sub BIN_VERSION_NV {

    sprintf "%d.%03d", BIN_MAJOR(), BIN_MINOR();

}

sub BIN_WRITE_VERSION_NV {

    sprintf "%d.%03d", BIN_MAJOR(), BIN_WRITE_MINOR();

}

#

# store

#

# Store target object hierarchy, identified by a reference to its root.

# The stored object tree may later be retrieved to memory via retrieve.

# Returns undef if an I/O error occurred, in which case the file is

# removed.

#

sub store {

    return _store(\&pstore, @_, 0);

}

#

# nstore

#

# Same as store, but in network order.

#

sub nstore {

    return _store(\&net_pstore, @_, 0);

}

#

# lock_store

#

# Same as store, but flock the file first (advisory locking).

#

sub lock_store {

    return _store(\&pstore, @_, 1);

}

#

# lock_nstore

#

# Same as nstore, but flock the file first (advisory locking).

#

sub lock_nstore {

    return _store(\&net_pstore, @_, 1);

}

# Internal store to file routine

sub _store {

    my $xsptr = shift;

    my $self = shift;

    my ($file, $use_locking) = @_;

    logcroak "not a reference" unless ref($self);

    logcroak "wrong argument number" unless @_ == 2;	# No @foo in arglist

    local *FILE;

    if ($use_locking) {

        open(FILE, ">>", $file) || logcroak "can't write into $file: $!";

        unless (&CAN_FLOCK) {

            logcarp

              "Storable::lock_store: fcntl/flock emulation broken on $^O";

            return undef;

        }

        flock(FILE, LOCK_EX) ||

          logcroak "can't get exclusive lock on $file: $!";

        truncate FILE, 0;

        # Unlocking will happen when FILE is closed

    } else {

        open(FILE, ">", $file) || logcroak "can't create $file: $!";

    }

    binmode FILE;	# Archaic systems...

    my $da = $@;	# Don't mess if called from exception handler

    my $ret;

    # Call C routine nstore or pstore, depending on network order

    eval { $ret = &$xsptr(*FILE, $self) };

    # close will return true on success, so the or short-circuits, the ()

    # expression is true, and for that case the block will only be entered

    # if $@ is true (ie eval failed)

    # if close fails, it returns false, $ret is altered, *that* is (also)

    # false, so the () expression is false, !() is true, and the block is

    # entered.

    if (!(close(FILE) or undef $ret) || $@) {

        unlink($file) or warn "Can't unlink $file: $!\n";

    }

    if ($@) {

        $@ =~ s/\.?\n$/,/ unless ref $@;

        logcroak $@;

    }

    $@ = $da;

    return $ret;

}

#

# store_fd

#

# Same as store, but perform on an already opened file descriptor instead.

# Returns undef if an I/O error occurred.

#

sub store_fd {

    return _store_fd(\&pstore, @_);

}

#

# nstore_fd

#

# Same as store_fd, but in network order.

#

sub nstore_fd {

    my ($self, $file) = @_;

    return _store_fd(\&net_pstore, @_);

}

# Internal store routine on opened file descriptor

sub _store_fd {

    my $xsptr = shift;

    my $self = shift;

    my ($file) = @_;

    logcroak "not a reference" unless ref($self);

    logcroak "too many arguments" unless @_ == 1;	# No @foo in arglist

    my $fd = fileno($file);

    logcroak "not a valid file descriptor" unless defined $fd;

    my $da = $@;		# Don't mess if called from exception handler

    my $ret;

    # Call C routine nstore or pstore, depending on network order

    eval { $ret = &$xsptr($file, $self) };

    logcroak $@ if $@ =~ s/\.?\n$/,/;

    local $\; print $file '';	# Autoflush the file if wanted

    $@ = $da;

    return $ret;

}

#

# freeze

#

# Store object and its hierarchy in memory and return a scalar

# containing the result.

#

sub freeze {

    _freeze(\&mstore, @_);

}

#

# nfreeze

#

# Same as freeze but in network order.

#

sub nfreeze {

    _freeze(\&net_mstore, @_);

}

# Internal freeze routine

sub _freeze {

    my $xsptr = shift;

    my $self = shift;

    logcroak "not a reference" unless ref($self);

    logcroak "too many arguments" unless @_ == 0;	# No @foo in arglist

    my $da = $@;	        # Don't mess if called from exception handler

    my $ret;

    # Call C routine mstore or net_mstore, depending on network order

    eval { $ret = &$xsptr($self) };

    if ($@) {

        $@ =~ s/\.?\n$/,/ unless ref $@;

        logcroak $@;

    }

    $@ = $da;

    return $ret ? $ret : undef;

}

#

# retrieve

#

# Retrieve object hierarchy from disk, returning a reference to the root

# object of that tree.

#

# retrieve(file, flags)

# flags include by default BLESS_OK=2 | TIE_OK=4

# with flags=0 or the global $Storable::flags set to 0, no resulting object

# will be blessed nor tied.

#

sub retrieve {

    _retrieve(shift, 0, @_);

}

#

# lock_retrieve

#

# Same as retrieve, but with advisory locking.

#

sub lock_retrieve {

    _retrieve(shift, 1, @_);

}

# Internal retrieve routine

sub _retrieve {

    my ($file, $use_locking, $flags) = @_;

    $flags = $Storable::flags unless defined $flags;

    my $FILE;

    open($FILE, "<", $file) || logcroak "can't open $file: $!";

    binmode $FILE;			# Archaic systems...

    my $self;

    my $da = $@;			# Could be from exception handler

    if ($use_locking) {

        unless (&CAN_FLOCK) {

            logcarp

              "Storable::lock_store: fcntl/flock emulation broken on $^O";

            return undef;

        }

        flock($FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!";

        # Unlocking will happen when FILE is closed

    }

    eval { $self = pretrieve($FILE, $flags) };		# Call C routine

    close($FILE);

    if ($@) {

        $@ =~ s/\.?\n$/,/ unless ref $@;

        logcroak $@;

    }

    $@ = $da;

    return $self;

}

#

# fd_retrieve

#

# Same as retrieve, but perform from an already opened file descriptor instead.

#

sub fd_retrieve {

    my ($file, $flags) = @_;

    $flags = $Storable::flags unless defined $flags;

    my $fd = fileno($file);

    logcroak "not a valid file descriptor" unless defined $fd;

    my $self;

    my $da = $@;				# Could be from exception handler

    eval { $self = pretrieve($file, $flags) };	# Call C routine

    if ($@) {

        $@ =~ s/\.?\n$/,/ unless ref $@;

        logcroak $@;

    }

    $@ = $da;

    return $self;

}

sub retrieve_fd { &fd_retrieve }		# Backward compatibility

#

# thaw

#

# Recreate objects in memory from an existing frozen image created

# by freeze.  If the frozen image passed is undef, return undef.

#

# thaw(frozen_obj, flags)

# flags include by default BLESS_OK=2 | TIE_OK=4

# with flags=0 or the global $Storable::flags set to 0, no resulting object

# will be blessed nor tied.

#

sub thaw {

    my ($frozen, $flags) = @_;

    $flags = $Storable::flags unless defined $flags;

    return undef unless defined $frozen;

    my $self;

    my $da = $@;			        # Could be from exception handler

    eval { $self = mretrieve($frozen, $flags) };# Call C routine

    if ($@) {

        $@ =~ s/\.?\n$/,/ unless ref $@;

        logcroak $@;

    }

    $@ = $da;

    return $self;

}

#

# _make_re($re, $flags)

#

# Internal function used to thaw a regular expression.

#

my $re_flags;

BEGIN {

    if ($] < 5.010) {

        $re_flags = qr/\A[imsx]*\z/;

    }

    elsif ($] < 5.014) {

        $re_flags = qr/\A[msixp]*\z/;

    }

    elsif ($] < 5.022) {

        $re_flags = qr/\A[msixpdual]*\z/;

    }

    else {

        $re_flags = qr/\A[msixpdualn]*\z/;

    }

}

sub _make_re {

    my ($re, $flags) = @_;

    $flags =~ $re_flags

        or die "regexp flags invalid";

    my $qr = eval "qr/\$re/$flags";

    die $@ if $@;

    $qr;

}

if ($] < 5.012) {

    eval <<'EOS'

sub _regexp_pattern {

    my $re = "" . shift;

    $re =~ /\A\(\?([xism]*)(?:-[xism]*)?:(.*)\)\z/s

        or die "Cannot parse regexp /$re/";

    return ($2, $1);

}

1

EOS

      or die "Cannot define _regexp_pattern: $@";

}

1;

__END__

=head1 NAME

Storable - persistence for Perl data structures

=head1 SYNOPSIS

 use Storable;

 store \%table, 'file';

 $hashref = retrieve('file');

 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);

 # Network order

 nstore \%table, 'file';

 $hashref = retrieve('file');	# There is NO nretrieve()

 # Storing to and retrieving from an already opened file

 store_fd \@array, \*STDOUT;

 nstore_fd \%table, \*STDOUT;

 $aryref = fd_retrieve(\*SOCKET);

 $hashref = fd_retrieve(\*SOCKET);

 # Serializing to memory

 $serialized = freeze \%table;

 %table_clone = %{ thaw($serialized) };

 # Deep (recursive) cloning

 $cloneref = dclone($ref);

 # Advisory locking

 use Storable qw(lock_store lock_nstore lock_retrieve)

 lock_store \%table, 'file';

 lock_nstore \%table, 'file';

 $hashref = lock_retrieve('file');

=head1 DESCRIPTION

The Storable package brings persistence to your Perl data structures

containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be

conveniently stored to disk and retrieved at a later time.

It can be used in the regular procedural way by calling C<store> with

a reference to the object to be stored, along with the file name where

the image should be written.

The routine returns C<undef> for I/O problems or other internal error,

a true value otherwise. Serious errors are propagated as a C<die> exception.

To retrieve data stored to disk, use C<retrieve> with a file name.

The objects stored into that file are recreated into memory for you,

and a I<reference> to the root object is returned. In case an I/O error

occurs while reading, C<undef> is returned instead. Other serious

errors are propagated via C<die>.

Since storage is performed recursively, you might want to stuff references

to objects that share a lot of common data into a single array or hash

table, and then store that object. That way, when you retrieve back the

whole thing, the objects will continue to share what they originally shared.

At the cost of a slight header overhead, you may store to an already

opened file descriptor using the C<store_fd> routine, and retrieve

from a file via C<fd_retrieve>. Those names aren't imported by default,

so you will have to do that explicitly if you need those routines.

The file descriptor you supply must be already opened, for read

if you're going to retrieve and for write if you wish to store.

	store_fd(\%table, *STDOUT) || die "can't store to stdout\n";

	$hashref = fd_retrieve(*STDIN);

You can also store data in network order to allow easy sharing across

multiple platforms, or when storing on a socket known to be remotely

connected. The routines to call have an initial C<n> prefix for I<network>,

as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be

correctly restored so you don't have to know whether you're restoring

from native or network ordered data.  Double values are stored stringified

to ensure portability as well, at the slight risk of loosing some precision

in the last decimals.

When using C<fd_retrieve>, objects are retrieved in sequence, one

object (i.e. one recursive tree) per associated C<store_fd>.

If you're more from the object-oriented camp, you can inherit from

Storable and directly store your objects by invoking C<store> as

a method. The fact that the root of the to-be-stored tree is a

blessed reference (i.e. an object) is special-cased so that the

retrieve does not provide a reference to that object but rather the

blessed object reference itself. (Otherwise, you'd get a reference

to that blessed object).

=head1 MEMORY STORE

The Storable engine can also store data into a Perl scalar instead, to

later retrieve them. This is mainly used to freeze a complex structure in

some safe compact memory place (where it can possibly be sent to another

process via some IPC, since freezing the structure also serializes it in

effect). Later on, and maybe somewhere else, you can thaw the Perl scalar

out and recreate the original complex structure in memory.

Surprisingly, the routines to be called are named C<freeze> and C<thaw>.

If you wish to send out the frozen scalar to another machine, use

C<nfreeze> instead to get a portable image.

Note that freezing an object structure and immediately thawing it

actually achieves a deep cloning of that structure:

    dclone(.) = thaw(freeze(.))

Storable provides you with a C<dclone> interface which does not create

that intermediary scalar but instead freezes the structure in some

internal memory space and then immediately thaws it out.

=head1 ADVISORY LOCKING

The C<lock_store> and C<lock_nstore> routine are equivalent to

C<store> and C<nstore>, except that they get an exclusive lock on

the file before writing.  Likewise, C<lock_retrieve> does the same

as C<retrieve>, but also gets a shared lock on the file before reading.

As with any advisory locking scheme, the protection only works if you

systematically use C<lock_store> and C<lock_retrieve>.  If one side of

your application uses C<store> whilst the other uses C<lock_retrieve>,

you will get no protection at all.

The internal advisory locking is implemented using Perl's flock()

routine.  If your system does not support any form of flock(), or if

you share your files across NFS, you might wish to use other forms

of locking by using modules such as LockFile::Simple which lock a

file using a filesystem entry, instead of locking the file descriptor.

=head1 SPEED

The heart of Storable is written in C for decent speed. Extra low-level

optimizations have been made when manipulating perl internals, to

sacrifice encapsulation for the benefit of greater speed.

=head1 CANONICAL REPRESENTATION

Normally, Storable stores elements of hashes in the order they are

stored internally by Perl, i.e. pseudo-randomly.  If you set

C<$Storable::canonical> to some C<TRUE> value, Storable will store

hashes with the elements sorted by their key.  This allows you to

compare data structures by comparing their frozen representations (or

even the compressed frozen representations), which can be useful for

creating lookup tables for complicated queries.

Canonical order does not imply network order; those are two orthogonal

settings.

=head1 CODE REFERENCES

Since Storable version 2.05, CODE references may be serialized with

the help of L<B::Deparse>. To enable this feature, set

C<$Storable::Deparse> to a true value. To enable deserialization,

C<$Storable::Eval> should be set to a true value. Be aware that

deserialization is done through C<eval>, which is dangerous if the

Storable file contains malicious data. You can set C<$Storable::Eval>

to a subroutine reference which would be used instead of C<eval>. See

below for an example using a L<Safe> compartment for deserialization

of CODE references.

If C<$Storable::Deparse> and/or C<$Storable::Eval> are set to false

values, then the value of C<$Storable::forgive_me> (see below) is

respected while serializing and deserializing.

=head1 FORWARD COMPATIBILITY

This release of Storable can be used on a newer version of Perl to

serialize data which is not supported by earlier Perls.  By default,

Storable will attempt to do the right thing, by C<croak()>ing if it

encounters data that it cannot deserialize.  However, the defaults

can be changed as follows:

=over 4

=item utf8 data

Perl 5.6 added support for Unicode characters with code points > 255,

and Perl 5.8 has full support for Unicode characters in hash keys.

Perl internally encodes strings with these characters using utf8, and

Storable serializes them as utf8.  By default, if an older version of

Perl encounters a utf8 value it cannot represent, it will C<croak()>.

To change this behaviour so that Storable deserializes utf8 encoded

values as the string of bytes (effectively dropping the I<is_utf8> flag)

set C<$Storable::drop_utf8> to some C<TRUE> value.  This is a form of

data loss, because with C<$drop_utf8> true, it becomes impossible to tell

whether the original data was the Unicode string, or a series of bytes

that happen to be valid utf8.

=item restricted hashes

Perl 5.8 adds support for restricted hashes, which have keys

restricted to a given set, and can have values locked to be read only.

By default, when Storable encounters a restricted hash on a perl

that doesn't support them, it will deserialize it as a normal hash,

silently discarding any placeholder keys and leaving the keys and

all values unlocked.  To make Storable C<croak()> instead, set

C<$Storable::downgrade_restricted> to a C<FALSE> value.  To restore

the default set it back to some C<TRUE> value.

The cperl PERL_PERTURB_KEYS_TOP hash strategy has a known problem with

restricted hashes.

=item huge objects

On 64bit systems some data structures may exceed the 2G (i.e. I32_MAX)

limit. On 32bit systems also strings between I32 and U32 (2G-4G).

Since Storable 3.00 (not in perl5 core) we are able to store and

retrieve these objects, even if perl5 itself is not able to handle

them.  These are strings longer then 4G, arrays with more then 2G

elements and hashes with more then 2G elements. cperl forbids hashes

with more than 2G elements, but this fail in cperl then. perl5 itself

at least until 5.26 allows it, but cannot iterate over them.

Note that creating those objects might cause out of memory

exceptions by the operating system before perl has a chance to abort.

=item files from future versions of Storable

Earlier versions of Storable would immediately croak if they encountered

a file with a higher internal version number than the reading Storable

knew about.  Internal version numbers are increased each time new data

types (such as restricted hashes) are added to the vocabulary of the file

format.  This meant that a newer Storable module had no way of writing a

file readable by an older Storable, even if the writer didn't store newer

data types.

This version of Storable will defer croaking until it encounters a data

type in the file that it does not recognize.  This means that it will

continue to read files generated by newer Storable modules which are careful

in what they write out, making it easier to upgrade Storable modules in a

mixed environment.

The old behaviour of immediate croaking can be re-instated by setting

C<$Storable::accept_future_minor> to some C<FALSE> value.

=back

All these variables have no effect on a newer Perl which supports the

relevant feature.

=head1 ERROR REPORTING

Storable uses the "exception" paradigm, in that it does not try to

workaround failures: if something bad happens, an exception is

generated from the caller's perspective (see L<Carp> and C<croak()>).

Use eval {} to trap those exceptions.

When Storable croaks, it tries to report the error via the C<logcroak()>

routine from the C<Log::Agent> package, if it is available.

Normal errors are reported by having store() or retrieve() return C<undef>.

Such errors are usually I/O errors (or truncated stream errors at retrieval).

When Storable throws the "Max. recursion depth with nested structures

exceeded" error we are already out of stack space. Unfortunately on

some earlier perl versions cleaning up a recursive data structure

recurses into the free calls, which will lead to stack overflows in

the cleanup. This data structure is not properly cleaned up then, it

will only be destroyed during global destruction.

=head1 WIZARDS ONLY

=head2 Hooks

Any class may define hooks that will be called during the serialization

and deserialization process on objects that are instances of that class.

Those hooks can redefine the way serialization is performed (and therefore,

how the symmetrical deserialization should be conducted).

Since we said earlier:

    dclone(.) = thaw(freeze(.))

everything we say about hooks should also hold for deep cloning. However,

hooks get to know whether the operation is a mere serialization, or a cloning.

Therefore, when serializing hooks are involved,

    dclone(.) <> thaw(freeze(.))

Well, you could keep them in sync, but there's no guarantee it will always

hold on classes somebody else wrote.  Besides, there is little to gain in

doing so: a serializing hook could keep only one attribute of an object,

which is probably not what should happen during a deep cloning of that

same object.

Here is the hooking interface:

=over 4

=item C<STORABLE_freeze> I<obj>, I<cloning>

The serializing hook, called on the object during serialization.  It can be

inherited, or defined in the class itself, like any other method.

Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating

whether we're in a dclone() or a regular serialization via store() or freeze().

Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized

is the serialized form to be used, and the optional $ref1, $ref2, etc... are

extra references that you wish to let the Storable engine serialize.

At deserialization time, you will be given back the same LIST, but all the

extra references will be pointing into the deserialized structure.

The B<first time> the hook is hit in a serialization flow, you may have it

return an empty list.  That will signal the Storable engine to further

discard that hook for this class and to therefore revert to the default

serialization of the underlying Perl data.  The hook will again be normally

processed in the next serialization.

Unless you know better, serializing hook should always say:

    sub STORABLE_freeze {

        my ($self, $cloning) = @_;

        return if $cloning;         # Regular default serialization

        ....

    }

in order to keep reasonable dclone() semantics.

=item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...

The deserializing hook called on the object during deserialization.

But wait: if we're deserializing, there's no object yet... right?

Wrong: the Storable engine creates an empty one for you.  If you know Eiffel,

you can view C<STORABLE_thaw> as an alternate creation routine.

This means the hook can be inherited like any other method, and that

I<obj> is your blessed reference for this particular instance.

The other arguments should look familiar if you know C<STORABLE_freeze>:

I<cloning> is true when we're part of a deep clone operation, I<serialized>

is the serialized string you returned to the engine in C<STORABLE_freeze>,

and there may be an optional list of references, in the same order you gave

them at serialization time, pointing to the deserialized objects (which

have been processed courtesy of the Storable engine).

When the Storable engine does not find any C<STORABLE_thaw> hook routine,

it tries to load the class by requiring the package dynamically (using

the blessed package name), and then re-attempts the lookup.  If at that

time the hook cannot be located, the engine croaks.  Note that this mechanism

will fail if you define several classes in the same file, but L<perlmod>

warned you.

It is up to you to use this information to populate I<obj> the way you want.

Returned value: none.

=item C<STORABLE_attach> I<class>, I<cloning>, I<serialized>

While C<STORABLE_freeze> and C<STORABLE_thaw> are useful for classes where

each instance is independent, this mechanism has difficulty (or is

incompatible) with objects that exist as common process-level or

system-level resources, such as singleton objects, database pools, caches

or memoized objects.

The alternative C<STORABLE_attach> method provides a solution for these